This invention relates to stabilizing blood-staining solutions which contain thiazine dyestuffs.
Differential blood stains have long been produced with the known staining solutions of Giemsa, May-Gruenwald, Leishman and Wright. A significant disadvantage of these staining solutions is that analytical results from different laboratories cannot be compared with one another owing to the variable quality of commercially available dyestuffs (J. Clin. Path. 28, 680 (1975)). Not only do large quality differences exist between dyestuffs of different manufacturers, but the dyestuffs are also subject to a chemical change with time. The staining solutions mentioned, owing to the lability in particular of the methylene blue molecule, which, in particular in an alkaline medium, degrades by oxidative demethylation into the next lower homolgues, i.e. azure A, azure B, azure C and thionine, cannot consistently be prepared in the same quality and therefore cannot be standardized either. The low stability of the solutions then gives rise to the formation of precipitations which simultaneously reduces the staining power of the solutions. In essence, the staining properties change due to a decrease in the optical density of the thiazine components, which is determined at about 645 nm. As a result, the blue/red color ratio undergoes a continuous shift, which after some time leads to stainings which are no longer acceptable. It is thus impossible to perform a standardization which, owing to increasing automation, is indispensable in this field.
Attempts have been made, then, to add stabilizers to the staining solutions to obtain reproducible staining power and constant color absorption and also to suppress precipitation. Additives which act as stabilizers are known from EP No. 49,833, EP No. 63,293 and EP No. 83,027. The stabilizing agents used therein are ammonium halides, primary, secondary or tertiary alkylamine hydrohalides or mixtures thereof. In these agents the halide is chloride, bromide or iodide. Hitherto, a preferred stabilizer has been diethylamine hydrochloride.